Pressure detecting instrument



y 21, 1964' D. F. HASTINGS 3,141,334

PRESSURE DETECTING INSTRUMENT I Filed Oct. 14, 1960 3 Sheets-Sheet 1 oIn M co

IN VEN TOR.

DONALD F. HASTINGS l 54w Md ATTORN S July 21, 1964 D. F. HASTINGS3,141,334

PRESSURE DETECTING INSTRUMENT Filed Oct. 14, 1960 s Sheets-Sheet 2 IN VEN TOR.

DONALD F. HASTINGS ATTORN YS D. F. HASTINGS PRESSURE DETECTINGINSTRUMENT 3 Sheets-Sheet 3 Filed Oct. 14, 1960 INVENTOR.

DONALD F. HASTINGS 15 MM ATTORNEZ United States Patent 3,141,334PRESSURE DETECTENG INSTRUMENT Donald F. Hastings, Suifern, N.Y.,assignor to The Bendix Corporation, Montrose, Pa., a corporation ofDelaware Filed Get. 14, 1960, Ser. No. 62,784 3 Claims. (Cl. 73-410)This invention relates to a measuring instrument having an armdisplaceable from an initial or zero position, said arm being springbiased against movement from such position. More particularly, theinvention relates to a novel arm mounting and biasing means.

The invention is shown herein in connection with a pressure measuringinstrument, as, for example, an oil pressure gauge for use with aninternal combustion engine, jet engine, or the like. It will be obvious,however, that the invention may be employed to advantage withinstruments of different types from the pressure gauge mechanism shownby way of illustration.

In prior apparatus of the type shown, a pressure responsive arm has beenmounted on the frame of theinstrument and spring biased against movementfrom its zero position by either a coil compression or a coil tensionspring. Such prior apparatus was not altogether satisfactory in yieldingaccurate pressure measurements over appreciable periods of use becauseof hysteresis of the spring. When instruments of the above-describedtype are mounted in proximity to a device such as an engine whichvibrates appreciably, the biasing springs of such instruments areadversely affected by the vibration, as is also true of the mechanism inthe instrument which pivotally mounts the arm. Both of such actionsseriously detract from the accuracy of the instrument, the former defectbeing generally the more serious since the usual instrument spring has alow resonant frequency lying well within the range of frequency ofvibration of the engine. A still further defect of the instrument iscaused by the fact that the arm biased by a coil compression or coiltension spring displays poor linearity over the range of measurementsfor which the instrument is designed.

It is accordingly among the objects of the present invention to providea force-measuring instrument provided with a novel measuring armsuspension which is but little affected by subjection to vibration.

A further object of the invention lies in the provision of aforce-measuring instrument having a measuring arm which is biased towardits zero position by a novel spring member, which has a very smallhysteresis, so that the instrument accurately returns to zero positionwhen unloaded.

Yet another object of the invention resides in the provision of a novelpressure-measuring instrument wherein the arm-biasing spring has a highresonant frequency, so that it is but little affected by being subjectedto normal engine vibrations, wherein the arm-biasing spring means has anexcellent linearity over the measuring range for which the instrument isdesigned, and wherein the measuring arm, the suspension means for thearm, and the biasing means for the arm present a substantially balancedconstruction.

A still further object of the invention lies in the provision of a novelsimple rugged and economical forcemeasuring instrument of the typedescribed.

The above and further objects and novel features of the invention willmore fully appear from the following description when the same is readin connection with the accompanying drawings. It is to be expresslyunderstood, however, that the drawings are for the purpose ofillustration only, and are not intended as a definition of the limits ofthe invention.

In the drawings, wherein like reference characters refer to like partsthroughout the several views,

FIG. 1 is a view in longitudinal generally axial section through theillustrative instrument, the section being taken in a plane displacedfrom the sectioning plane of FIG. 2, certain of the parts being shown inside elevation;

FIG. 2 is a view in longitudinal generally axial section through theillustrative instrument, the section being taken in a plane displaced 90from the sectioning plane of FIG. 1, certain of the parts being shown inside elevation;

FIG. 3 is a view in transverse section through an intermediate portionof the instrument, the section being taken generally along the line 3-3of FIG. 2, the synchronous generator of the instrument being shown inphantom lines for clarity of illustration;

FIG. 4 is a view in transverse section through the instrument showingthe driving mechanism between the measuring arm and the generator, thesection being taken along the line 4--4 of FIG. 2;

FIG. 5 is a fragmentary view in longitudinal section through the meansfor adjusting the instrument to its initial or zero position, certain ofthe parts being shown in side elevation, the section being taken alongline 55 of FIG. 4;

FIG. 6 is a fragmentary view in side elevation of a portion of the frameof the instrument at one of the ieans for clampingly retaining an end ofthe torque rod mounting the measuring arm of the instrument; and

FIG. 7 is a fragmentary view in cross section of the driving mechanismfor the indicating device, the section being taken along line 7-7 ofFIG. 4.

The instrument shown by way of illustration, which is generallydesignated by the reference character 10, is adapted for use inmeasuring the oil pressure of an engine and for transmitting the readingof the pressure in the form of a signal from a synchronous generator orsynchro to an appropriate visually read meter or recording device (notshown). The instrument shown, which is designed for mounting inproximity to an engine, is mounted in an hermetically sealed casingformed of a transverse head member 11, an end or bottom member 12, and acircular cylindrical shell 14 which is edgewelded to members 11 and 12.Head member 11 forms a portion of the frame of the instrument, therebeing a further transverse plate member 15 mounted within casing 14 andrigidly connected to member 11 by a series of spaced columns 16 havingtheir ends connected to members 11 and 15 as shown.

Member 11 is provided with an inlet fitting 17 to which the lubricatingoil under pressure for the engine is led. Fitting 17 communicates with asleeve 19 integrally connected thereto inwardly of the casing, 21flexible tube 20 leading from the sleeve 1 to the fixed base portion ofa first longitudinally expansible chamber in the form of a bellows 21having a thin circumferentially pleated wall. Chamber 21 has one endthereof fixedly secured to transverse member 15 by a base member 23.Chamber 21 expands longitudinally upon increase of pressure in the fluidfed thereto, and decreases in length when such fluid pressure decreases.The movable end of bellows 21 is connected to a first arm 45 of ameasuring lever 26, to be described. The instrument shown is designed toyield a pressure reading equal to the amount which the pressure of thefluid exceeds atmospheric pressure. There is therefore provided withinthe housing a second expansible chamber 22 which is identical withchamber 21 but the interior of which communicates with the atmospherethrough a tube 24 connected to the fixed end thereof, the outer end ofsuch tube opening through end closure member 12 within an open endedprotective hood 25. Chamber 22 has one end thereof fixedly mounted tomember E through a support 28 affixed to such member, as shown. Themovable end of chamber 22 is connected to a second, oppositely disposedarm 46 of the measuring lever 26, so that the expansive forces operativeupon chambers 21 and 22 are always in opposition.

The measuring lever 26, which is mounted for oscillation about the axisof a torque rod 32, is drivingly connected to a synchronous generator orsynchro 27 through motion-multiplying mechanism 29. The angulardisplacement of lever 26 is thus refiected in rotation of the rotor ofthe synchro, the output of the synchro being led to a suitablycalibrated instrument. The output wires 30 on the synchro are brought toa first fixed part 31 of a separable electrical connector which issecured and sealed to the end member 12 of the casing.

The novel mounting and biasing means for the lever 26 is shown in FIGS.1, 2, 3, and 6. Such means includes a torque rod 32 extendingdiametrally of the casing adjacent end member 11, rod 32 serving both toallow the lever to pivot or oscillate through a limited range and alsoto oppose such oscillation from a central, at rest or zero position.Lever 26 has a thickened terminal hub portion which is inwardly groovedto receive an enlarged splined intermediate portion of rod 32 to form arigid connection therewith. Splined connection 34 may be made by pressfitting the parts together.

Opposed portions of end member 11 extend inwardly of the casing somewhatto form ears 35 and 46. Each of such ears is provided with a V groovewhich converges in the direction of the main portion of member 11, thegroove in ear 35 being designated 36 and that in ear 40 being designated41. Opposite ends of torque rod 32 are enlarged at 37 and 42, so as tobe clamped within the V grooves 36 and 41. To improve the grippingengagement between the parts, it is preferred that enlargements 37 and42 be roughened as by being sandblasted before being assembled in theinstrument. The torque rod is retained in the position shown by means ofstrap-like members which bridge the ends of the V grooves, and press theends of the torque rods firmly into such grooves. The strapmember-engaging enlarged end 37 of the rod, designated 39, is retainedon ear 35 by machine screws 38; the member 44 retaining enlarged end 42of rod 32 is retained on ear 46 by machine screws 43. The describedstructure retains the ends of torque rod 32 from turning with respect tothe frame of the instrument, so that turning of measuring lever 26 fromits neutral or zero position causes rod 32 to twist. Rod 32, therefore,functions both to mount lever 26 for pivotal movement and alsoconstantly to spring bias it toward its zero position.

The measuring lever 26 is generally of T shape, the two previouslydescribed arms 45 and 46 forming the top of the T. Lever 26 has a maingenerally radiallyextending arm 47 through which connection is made byway of the mechanism 29 to the synchro 27. Ann 47 has a lower endportion'49 in the form of a spring metal strap carrying a driving pin56. The position of pin 50 relative to the axis of the casing, wherebyto adjust the ratio of motion-multiplication afforded by mechanism 29,may be changed within limits by the adjusting stud 51. An adjustablestop for lever 47 is provided in the form of a threaded stud 52positioned in a threaded bore in bellows-supporting member 23, as shownin FIG. 1.

The motion-multiplying mechanism 29 includes an oscillatable platemember 54 which is mounted parallel to intermediate supporting plate 15and is rotatably secured thereto by a journal bearing 55. The synchro27, as shown in FIG. 2, has the casing thereof connected to end platemember 15 so that it may be adjusted about the axis of the synchro andthen held fixedly with respect thereto. Plate 54 has a longitudinalextension 56 (FIG. 1) and an overarm 57 connected thereto. Between themain portion of plate member 54 and the overarm 57 there is pivotallymounted a sector member 61. Member 61 is carried upon pintle pins 59 and6th in overarm 57 a and the main portion of plate member 54,respectively, as shown in FIG. 2.

Sector member 61 has a sector gear 62 thereon meshing with a pinion 64on the end of the shaft of the synchro 27. A helically wound hairspring65, connected at its outer end to a post on plate member 54 and at itsinner end to the shaft of the synchro 27, maintains the teeth of sectorgear 62 and pinion 64 in contact at all times. It will be apparent thata relatively small angular motion of sector 61 will result in a veryconsiderable angular motion of the rotor of synchro 27. Sector 61 isdriven by the aforesaid pin 50, such pin being accurately receivedbetween opposed parallel arms 66 affixed to sector 61. It will be seenthat adjustment of the position of pin 50 relative to pintle pins 59 and66 about which sector 61 oscillates will change the effective ratio ofmotion-multiplication between arm 47 and sector 61.

In the illustrative embodiment there is shown a simple effectivemechanism whereby the instrument may be adjusted as required to aninitial or Zero setting without disturbing the hermetic seal of thecasing of the instrument. Such adjustment is effected by rotating thecasing and thus the stator of the syncho 27 relative to the rotorthereof by rotation of the plate 54 upon which the synchro is mounted.Plate 54 has a lateral extension arm 70 to which the zero adjustingmeans 71 is connected. The construction of means 71 and its relation toarm 70 will be more readily understood on consideration of FIGS. 1 and5.

A hollow longitudinally-extending shell 72 is afiixed and sealed to endclosure member 12 as shown. Mounted within shell 72 and sealed theretois an adjusting mechanism 74 including an inner shell 75 having anenlarged head 76 which extends inwardly of the main housing of theinstrument and an outer end which is exposed to the atmosphere at theouter end of shell 72. Inner shell 75 has a threaded axial passage 77therein at its intermediate and outer portions and a shallow ball seat81 at its inner end. A longitudinally extending adjusting levergenerally designated 79 has an intermediate ball member 80 mountedwithin ball seat 81. Adjusting lever 79 has a rear or outer arm 82thereon, arm 82 terminating in a smaller ball 34. Lever 79 has aforwardly-extending arm 85 which is attached at its outer end to theinner end member 86 of a sealing pleated bellows 37. The outer or rearend of bellows 87 is sealed to the inner end of the inner shell member75. Secured to member 86 is a second similar member 96 which has aninwardly projecting ball 89 positioned centrally thereof. Ball 89 fitswithin an angularly directed slot 91 in arm 70, the direction of slot 91being such that oscillation of ball 89 in a vertical plane (FIGS. 4 and5) will cause oscillation of member 54 about journal 55.

Oscillation of adjusting lever 79 from a position external of thehousing of instrument 10 is effected by an externally threaded internalnut 92 which is threadedly received in bore 77 of shell 75. Nut 92 hasan eccentrically disposed longitudinally-extending bore 94 therein, suchbore accurately receiving the ball 84 on the outer arm of adjustinglever 79. Nut 92 may be turned, after removal of the protective plug 95,as by inserting a screw driver into slots on the outer end of the nut.After the nut has been turned sufiiciently to turn the rotor of thesynchro to the desired zero position, the nut 92 may be locked in placeby reinserting the protective plug 95. The flexible bellows 87 permitsthe required motion of adjusting lever 79 and thus of ball 89, whilepreserving an hermetic seal across the inner end of the shell 75.

In order substantially to eliminate play between driving pin 50 and theopposed parallel arms 66 affixed to sector 61, there is provided thefollowing adjusting mechanism for arms 66. Such arms are in the form ofparallel pins projecting inwardly from an enlarged head 96 on a rod-likemember 97 which is rotatably mounted in a bore 98 in member 57. Pins 66are spaced from each other a distance which slightly exceeds thediameter of driving pin 50. The rear end of member 97 projectsrearwardly of member 57, so as to allow the rotation of the former byones fingers when member 97 is free for rotation, so that play betweenpin 50 and each of pins 66 may be entirely taken up, as indicated inFIG. 7. A setscrew 100 threaded into member 57 and intersecting bore 98permits member 97 to be securely retained in its thus adjusted position.

Although only one embodiment of the invention has been illustrated inthe accompanying drawings and described in the foregoing specification,it is to be expressly understood that various changes, such as in therelative dimensions of the parts, materials used, and the like, as wellas the suggested manner of use of the apparatus of the invention, may bemade therein without departing from the spirit and scope of theinvention as will now be apparent to those skilled in the art.

What is claimed is:

1. In a pressure differential indicating device, a hermetically sealedcasing, a pair of expansible chamber means in said casing and externallysubjected to the pressure within the casing, means connecting theinteriors of said chamber means to diiferent sources of fluid pressure,a substantially rigid, torsionally-resilient bar fixedly securedadjacent each end thereof, lever means secured to said bar intermediatethe ends of the latter, whereby said bar resiliently resists angularmovement of the lever means about the axis of the bar in eitherdirection from a null position determined by the relaxed position of thebar, means for operatively so connecting said pair of chamber means tosaid lever means that fluid pressure within one of said chamber meanstends to twist said bar in one direction about its axis and pressurewithin the other chamber means simultaneously tends to twist said bar inthe opposite direction, whereby the bar is subjected to a torquedetermined by the diiferential between the pressures within said pair ofchamber means, a synchronous generator having a rotor, means operativelyconnecting said lever means and rotor, whereby angular movement of therotor by said lever means is indicative of the degree and direction oftwist of said bar from said relaxed position thereof, and meansrotatable from outside the sealed casing for adjusting said connectingmeans to efiect a zero setting of said rotor relative to said levermeans.

2. An indicating device as defined in claim 1 wherein each of saidchamber means comprises a resilient bellows.

3. An indicating device as defined in claim 1 wherein said lever meanscomprises arms extending radially from said bar at opposite sidesthereof in a common transverse plane.

References Cited in the file of this patent UNITED STATES PATENTS1,827,560 Binckley Oct. 13, 1931 2,365,573 McGay Dec. 19, 1944 2,625,820Whitehead et al Jan. 20, 1953 2,707,397 Grover May 3, 1955 2,788,664Coulbourn et a1. Apr. 16, 1957 2,816,444 Gomez Dec. 17, 1957

1. IN A PRESSURE DIFFERENTIAL INDICATING DEVICE, A HERMETICALLY SEALEDCASING, A PAIR OF EXPANSIBLE CHAMBER MEANS IN SAID CASING AND EXTERNALLYSUBJECTED TO THE PRESSURE WITHIN THE CASING, MEANS CONNECTING THEINTERIORS OF SAID CHAMBER MEANS TO DIFFERENT SOURCES OF FLUID PRESSURE,A SUBSTANTIALLY RIGID, TORSIONALLY-RESILIENT BAR FIXEDLY SECUREDADJACENT EACH END THEREOF, LEVER MEANS SECURED TO SAID BAR INTERMEDIATETHE ENDS OF THE LATTER, WHEREBY SAID BAR RESILIENTLY RESISTS ANGULARMOVEMENT OF THE LEVER MEANS ABOUT THE AXIS OF THE BAR IN EITHERDIRECTION FROM A NULL POSITION DETERMINED BY THE RELAXED POSITION OF THEBAR, MEANS FOR OPERATIVELY SO CONNECTING SAID PAIR OF CHAMBER MEANS TOSAID LEVER MEANS THAT FLUID PRESSURE WITHIN ONE OF SAID CHAMBER MEANSTENDS TO TWIST SAID BAR IN ONE DIRECTION ABOUT ITS AXIS AND PRESSUREWITHIN THE OTHER CHAMBER MEANS SIMULTANEOUSLY TENDS TO TWIST SAID BAR INTHE OPPOSITE DIRECTION, WHEREBY THE BAR IS SUBJECTED TO A TORQUEDETERMINED BY THE DIFFERENTIAL BETWEEN THE PRESSURES WITHIN SAID PAIR OFCHAMBER MEANS, A SYN-